The psychomotor slowing is a commonly observed indicator of aging, organic brain damage and functional behavioral disorders. The most frequently used research paradigm, i.e. the reaction time, however, can not be used for the clinical purpose of separating these groups efficiently. The reason is both in that reaction time as a score is too variable, and the task is too complex to be reduced to a single numerical value. In order to increase our understanding the internal mechanisms of the reaction time (RT), we developed a technique for the microbehavioral analysis of the choice RT response. In our first study we were able to show that when both hands are observed, several distinct motor events preceding the response can be recorded. They can be interpreted as behavioral equivalents of attentional adjustments, comprehension and decision making processes. Also, the response itself provides several parameters reflecting directly on the efficiency of psychomotor performance. The study described in this proposal will examine the simple and choice RT performance in three clinical groups, i.e. depressives, senile dementia and normal aged. The study consists of four experiments. The first three are designed to provide a more detailed understanding of the response generation mechanisms, and the fourth experiment represents a clinical validation of the microbehavioral approach. After completing this study we should be able to specify accurately the optimal test procedure which could be used as a precise and sensitive clinical tool for assessment of psychomotor impairment in elderly patients and to extend the research to clinical groups of elderly other than those with senile dementia or depression.